WASHINGTON — The number of Americans who filed applications for unemployment benefits sank last week to the lowest level since early spring, but a government official suggested the surprising drop may have stemmed from “technical” issues not captured by normal seasonal adjustments.

Jobless claims fell by 37,000 to 391,000 in the week ended Sept. 24, putting them at the lowest level since April 2, the Labor Department reported Thursday. Initial claims from two weeks ago were revised up to 428,000 from an original reading of 423,000.

Economists surveyed by MarketWatch had expected new claims to fall to 417,000 on a seasonally adjusted basis.

A Labor official said 2011 was an unusual calendar year that made seasonal adjustments harder to calculate. The government’s data may also have been affected by recent holidays and several major storms, he said.

What is less clear is whether the sharp drop in claims can be sustained over the next few weeks. Historical data suggests they could rise again.

The average of new claims over the past four weeks fell by a much smaller 5,250 to 417,000. The monthly average is seen as a more accurate gauge of labor trends because it smooths out volatility in the week-to-week data.

Reflecting a weak jobs market, claims had hovered around the 425,000 mark for the past six months. Claims usually fall near the 300,000 level in periods of strong economic growth.

Over the past three months, the economy has gained an average of less than 35,000 jobs, far below the level needed to make a dent in the unemployment rate.

The lack of hiring spurred Federal Reserve Chairman Ben Bernanke on Wednesday to call for Washington to enact bipartisan policies to bolster the economy. He called the nation’s persistently high unemployment rate — 9.1 percent in August — a “national crisis.”

Hiring is not expected to pick up anytime soon, particularly given renewed fears of another recession and fresh worries about a financial crisis in Europe.

In September, for example, economists surveyed by MarketWatch project that only 83,000 jobs were created. The monthly employment report will be issued on Oct. 7.

Economists say hiring would have to average 250,000 a month for several years to pull the nation’s jobless rate back down to pre-recession levels.

The number of Americans who continue to receive regular state unemployment checks, meanwhile declined by 20,000 to 3.73 million in the week ended Sept. 17. Continuing claims are reported with a one-week lag.

About 6.98 million people received some kind of state or federal benefit in the week of Sept. 10, up 95,242 from the prior week. Total claims are reported with a two-week lag.

The federal government offers extended compensation to millions of Americans whose state benefits have already expired. Benefits in most states last six months.